No, the first one was really repetitive to the point of being boring, but the second and Brotherhood are very good about being varied and very interesting. I can't comment for the newer ones, haven't played them yet.

AC2 is night and day compared to AC1. It takes the good core concepts, ditches the idiotic stuff, and adds tons of new stuff. AC1 was a glitchy mess but I powered through because I don't play sequels without knowing the story of the first game. AC2 is, simply, MUCH better.

I Disnt think AC1 was all that repetitive, the biggest part was riding the horse out of masyaf every time. AC2 though is so different. I Played not knowing how far i was into the game, or how close i was to the end, every assassination is different and is all worked into the story and the world, its nothing like "go kill several people and then you'll get the boss", ezio even has a chart of the people he is going after and it goes off in several directions and new people appear who you didnt expect would show up. One of the DLC's for AC2 has something similar to AC1 where you have to kill 9 lieutenants for another character. ACB and ACR are kinda repetitive in the way that you need to destroy enemy towers (double as being viewpoints) and taking territory form them, ACR has a decent minigame where you defend your place from bad guys